1. Field of the Invention
The present invention generally relates to a library apparatus and so on which contains storage media such as a magnetic tape library apparatus, and particularly relates to a medium transport apparatus which detects a deflection amount when a deflection arises in a mechanism transporting a cartridge to a rack (cell) of a cartridge-type storage medium (hereinafter referred to as a cartridge), and enables accurate cartridge insertion and withdrawal to and from the cell by correcting its error.
2. Description of the Related Art
FIGS. 11A to 11C illustrate conventional techniques. In FIG. 11A, reference numeral 2 denotes a media storage cell which contains a number of media 3 such as cartridges which are to be transported. A mechanism which takes the medium 3 in and out of the media storage cell 2, and transports the medium 3 includes a hold unit 16 equivalent to a robot hand for holding the medium 3, an arm unit 15 which moves the hold unit 16 horizontally, a support unit 18 which supports the arm unit 15, and an LM rail 19 for guiding the support unit 18 and moving the support unit 18 vertically. Additionally, although not shown, each servomotor is incorporated in the hold unit 16, support unit 18 and so on.
For alignment of the hold unit 16 with the media storage cell 2, a conventional magnetic tape library apparatus with a transport mechanism (transfer robot) as shown in FIG. 11A has, for example, as shown in FIG. 11B, reference flags F1 and F2 arranged in two places in cells in both the right and left ends of the media storage cell 2, reads these flag positions using a sensor mounted in the hold unit 16, detects horizontal and vertical errors from a nominal position, and corrects linearly a relative phase error between each cell and the transfer robot using the error amount.
Additionally, as conventional techniques which determine or correct a position of a transfer robot, there are, for example, a position data correction method disclosed in Japanese Patent Laid-Open No. 5-342723, and an object position determination system disclosed in Japanese Patent Laid-Open No. 2000-314611. The technique disclosed in Japanese Patent Laid-Open No. 5-342723 is characterized in that, so as to make it possible to correct position data used for positioning control of a servo motor in high precision with a small error, data capturing for correcting position data is performed in a pitch from a reference target flag, which becomes a positioning target, to a next target flag which is adjacent to it. However, in Japanese Patent Laid-Open No. 5-342723, it is not considered at all to measure a deflection amount of an arm of the transfer robot in advance, and to perform correction based on the deflection amount.
Additionally, the technique of Japanese Patent Laid-Open No. 2000-314611 images a guide target having a shape of a right angled triangle, calculates a distance from a vertex angle by calculating a position of a point at which a scanning line intersects a base of the right angled triangle, and guides a medium handler based on the distance, for proper alignment between the medium handler and a magazine slot. This does not also take account of measuring a deflection amount of an arm in advance and performing correction based on the deflection amount.
As shown in FIG. 11A, when a transfer robot is cantilevered, a deflection may arise in the arm unit 15 owing to weight of the hold unit 16 and so on, and its deflection amount may become remarkable as a tip approaches. In this case, as shown in FIG. 11C, an error arises in a relative position error itself between a cell and the transfer robot which is detected by a conventional method, and consequently, it becomes impossible to achieve accurate insertion and withdrawal of the medium 3 to and from the cell which is to be a target. Additionally, in FIG. 11C, P11, P12, and P13 show errors of center positions of respective cells which are detected by the conventional method, and P1, P2, and P3 show actual position errors due to the deflection of the arm unit 15.